HHistorically centered on energy production and its decarbonization, the public debate has integrated the issue of sobriety. The war in Ukraine highlighting our dependence on Russian fossil fuels obviously contributes to this development. But what exactly are we talking about? And how to implement it?
The starting point is simple: energy is not directly useful to us. It becomes so when we combine it with a machine providing an energy service: a boiler to heat our home, a car to go on vacation, a lamp to give us light, a smartphone to connect us to social networks, etc.
Two strategies are then available to reduce energy consumption: reduce the use of the service, or invest in machines that consume less energy for the same level of service. Concretely, reducing our trips or buying a car that consumes less fuel, lowering the temperature inside our apartment or insulating it. Conceptually, reducing our uses or investing in energy efficiency.
The energy impact of reducing usage obviously depends on the type of action and the vigor with which it is implemented. Reducing the temperature of your home by one degree reduces energy consumption by 7%. And therefore double if we go from 20 degrees – the average in French housing – to 18 degrees. Limiting your speed to 110 km/h on the highway would reduce the amount of fuel consumed on the journey by 20%. A carpool can do much better.
Rebound effect
Investing in energy efficiency has a more complex effect on energy consumption. A more efficient machine will in fact see its energy cost of use reduced. It will then be used more often. The purchase of a car that consumes less fuel per kilometer will allow its user to make more trips, the energy renovation of a dwelling will encourage its occupants to increase the interior temperature in winter.
Part of the energy benefit of the investment will thus be dissipated in an increase in use. This is the rebound effect. Will it negate the energy benefit? Expressed another way, will the energy consumption exceed that observed before the investment? A positive answer to these questions would make the energy efficiency strategy irrelevant.
Economic research has come a long way in measuring the magnitude of the rebound effect. The results are available for different sectors (building renovation, car traffic, industry), and they are unambiguous: the rebound does indeed exist, but it does not cancel out the energy benefits of the investment (see , for example, the synthesis of these results carried out by Gillingham, Rapson and Wagner in 2016).
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